Liquid crystal display

ABSTRACT

Disclosed is a liquid crystal display comprising a first substrate including wiring, which intersects to define unit pixels, and a first electrode formed in each unit pixel; a second substrate provided opposing the first substrate at a predetermined distance and including a second electrode formed over an entire surface of the second substrate, the second electrode generating an electric field with the first electrode; and a liquid crystal layer injected between the first substrate and the second substrate and including liquid crystal molecules that are horizontally oriented in one direction, the liquid crystal molecules, as a result of the electric field generated between the first and second substrates, having a symmetrically bent alignment about an imaginary center plane parallel to the first and second substrates at a center position therebetween, wherein the first electrode is protruded in a direction toward the second substrate at edges where orientation for the liquid crystal molecules starts.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a liquid crystal display, and moreparticularly, to a liquid crystal display having a bent alignment ofliquid crystal molecules to obtain a wide viewing angle and a fastresponse time.

(b) Description of the Related Art

Liquid crystal displays typically include a first substrate havingcommon electrodes and a color filter, and a second substrate having thinfilm transistors and pixel electrodes. The first substrate and thesecond substrate are provided substantially in parallel with apredetermined gap therebetween, and liquid crystal is injected betweenthe two opposing substrates. An electric field is formed between thesubstrates by applying different voltages to the pixel electrodes andcommon electrodes. Accordingly, the alignment of liquid crystalmolecules of the liquid crystal material is varied to thereby controlthe transmittance of incident light.

Various types of liquid crystal displays have been developed to improveresponse times and viewing angle. They include the HAN (hybrid alignednematic) mode liquid crystal display and the OCB (optically compensatedbend) mode liquid crystal display. The OCB mode LCD includes anelectrode formed on each opposing substrate, the electrodes acting toform an electric field that is perpendicular to the two substrates;liquid crystal injected between the two substrates; and an alignmentlayer formed on each substrate, the alignment layers providing a forceto align the liquid crystal molecules in a direction substantiallyparallel to the two substrates.

In the OCB mode LCD, a symmetrical arrangement is realized about animaginary center plane between the two substrates and parallel to thesame. That is, the liquid crystal molecules are aligned substantiallyparallel to the substrates, then are increasingly slanted until reachingthis center plane where the liquid crystal molecules are substantiallyperpendicular to the two substrates. A wide viewing angle is achieved asa result. To obtain such a bent alignment of the liquid crystalmolecules, a horizontal alignment agent that is oriented in the samedirection is used and a high voltage is initially applied. Also, sincethe liquid crystal molecules move in the same orientation when the LCDis operated, a wide viewing angle and a fast response time are realized.

However, in such a LCD, in areas where unit pixels begin, a smoothbending alignment of the liquid crystal molecules cannot be aligned in asmooth bending pattern, thereby limiting the display characteristics.This is a result of the opposing directions of the bending alignment ofthe liquid crystal molecules and the bending direction of the electricfield at edges of the pixel electrodes. That is, unlike the commonelectrode, which is formed over an entire surface of the substrate, thepixel electrodes are divided for each pixel region such that thisopposing direction of LC molecule alignment and electric field occurs atthe edges of the pixel electrodes.

SUMMARY OF THE INVENTION

The present invention has been made in an effort to solve the aboveproblems.

It is an object of the present invention to provide a liquid crystaldisplay that realizes a stable bent alignment of liquid crystalmolecules such that a wide viewing angle and fast response times areobtained.

To achieve the above object, the present invention provides a liquidcrystal display comprising a first substrate including wiring, whichintersects to define unit pixels, and a first electrode formed in eachunit pixel; a second substrate provided opposing the first substrate ata predetermined distance from the same, and including a second electrodeformed over an entire surface of the second substrate, the secondelectrode generating an electric field with the first electrode; and aliquid crystal layer injected between the first and second substratesand including liquid crystal molecules that are horizontally oriented inone direction, the liquid crystal molecules, as a result of the electricfield generated between the first and second substrates, having asymmetrically bent alignment about an imaginary center plane parallel tothe first and second substrates at a center position therebetween,wherein the first electrode is protruded in a direction toward thesecond substrate at edges where orientation for the liquid crystalmolecules starts.

According to a feature of the present invention, a protrusion pattern isformed under the first electrode.

According to another feature of the present invention, a thickness ofthe protrusion pattern is 1-4 μm.

According to yet another feature of the present invention, the wiringincludes gate lines for transmitting gate signals, and data linesintersecting the gate lines and transmitting image signals.

According to still yet another feature of the present invention, theliquid crystal display further comprises storage capacitance wiringformed on a same layer as the gate lines but separated from the same,the storage capacitance wiring overlapping the first electrode.

According to still yet another feature of the present invention, thefirst substrate includes a thin film transistor having a gate electrodeformed at areas where the gate lines intersect the data lines andconnected to the gate lines, a source electrode connected to the datalines, a drain electrode opposing the source electrode with respect thegate electrode, and a semiconductor layer.

According to still yet another feature of the present invention, theprotrusion pattern is formed on a same layer as organic insulationmaterial, the gate lines, or the semiconductor layer.

According to still yet another feature of the present invention, firstand second orientation layers are formed respectively on the first andsecond substrates, the orientation layers providing an orienting forceto the liquid crystal molecules in an identical direction horizontal tothe substrates.

According to still yet another feature of the present invention, theliquid crystal layer has a positive anisotropic dielectricity.

In another aspect, the present invention provides a liquid crystaldisplay comprising a first substrate including wiring, which intersectsto define unit pixels, and a first electrode formed in each unit pixel;a second substrate provided opposing the first substrate at apredetermined distance from the same, and including a second electrodeformed over an entire surface of the second substrate, the secondelectrode generating an electric field with the first electrode; aliquid crystal layer injected between the first and second substratesand including liquid crystal molecules that are horizontally oriented inone direction, the liquid crystal molecules, as a result of the electricfield generated between the first and second substrates, having asymmetrically bent alignment about an imaginary center plane parallel tothe first and second substrates at a center position therebetween; and aprotrusion pattern formed on the first substrate or second substrate,the protrusion pattern forming a slanted surface that opposes anorientation direction at edges of the unit pixels where orientation ofthe liquid crystal molecules begins or ends.

According to a feature of the present invention, the liquid crystalmolecules have a larger pretilt angle with respect to the first andsecond substrates at the edges of the unit pixels than at other areas.

According to another feature of the present invention, the wiringincludes gate lines for transmitting gate signals, and data linesintersecting the gate lines and transmitting image signals.

According to yet another feature of the present invention, the firstsubstrate includes a thin film transistor having a gate electrode formedat areas where the gate lines intersect the data lines and connected tothe gate lines, a gate insulation layer covering the gate electrode, asemiconductor layer formed over the gate insulation layer, a sourceelectrode connected to the data lines, and a drain electrode opposingthe source electrode with respect the gate electrode.

According to still yet another feature of the present invention, theprotrusion pattern is formed on a same layer as organic insulationmaterial, the gate lines, the semiconductor layer, or the data lines.

According to still yet another feature of the present invention, whereinthe liquid crystal display further comprises storage capacitance wiringformed on a same layer as the gate lines but separated from the same,the storage capacitance wiring overlapping the first electrode.

According to still yet another feature of the present invention, theprotrusion pattern forms a depression on the first and second substratesat edges of the unit pixels where orientation of the liquid crystalmolecules starts.

According to still yet another feature of the present invention, theprotrusion pattern is formed on the first and second substrates at edgesof the unit pixels where orientation of the liquid crystal moleculesends.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate an embodiment of the invention,and, together with the description, serve to explain the principles ofthe invention:

FIG. 1 is a schematic plan view of a TFT substrate used in a liquidcrystal display according to a first preferred embodiment of the presentinvention;

FIG. 2 is a sectional view taken along line II-II′ of FIG. 1;

FIG. 3 is a schematic plan view of a TFT substrate used in a liquidcrystal display according to a second preferred embodiment of thepresent invention;

FIG. 4 is a sectional view taken along line IV-IV′ of FIG. 3;

FIG. 5 is a sectional view of a liquid crystal display according to athird preferred embodiment of the present invention;

FIG. 6 is a sectional view of a liquid crystal display according to afourth preferred embodiment of the present invention;

FIG. 7 is a schematic plan view of a TFT substrate used in a liquidcrystal display having independent storage capacitance wiring accordingto a fifth preferred embodiment of the present invention; and

FIG. 8 is a sectional view taken along line VIII-VIII′ of FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail with reference to the accompanying drawings.

In the present invention, in order to obtain a stable bent alignment ofliquid crystal molecules, a structure of electrodes is altered such thata direction of an electric field corresponds to a bent alignmentdirection or orientation direction of the liquid crystal molecules, or apretilt angle of the liquid crystal molecules is raised by the formationof grooves or protrusions.

FIG. 1 shows a schematic plan view of a TFT substrate used in a liquidcrystal display according to a first preferred embodiment of the presentinvention, and FIG. 2 shows a sectional view taken along line II-II′ ofFIG. 1. A color filter substrate is shown together with the TFTsubstrate in FIG. 2.

The liquid crystal display includes a lower substrate 100 (the TFTsubstrate) and an upper substrate 200 (the color filter substrate). Thelower and upper substrates 100 and 200 are positioned substantially inparallel with a predetermined gap therebetween. The lower substrate 100includes a lower insulation substrate 10, and gate wiring formed of alow-resistance conductive material over the insulation substrate 10. Thegate wiring includes gate lines 22 extended horizontally (in FIG. 1) andgate electrodes 26 of a thin film transistor, the gate electrodes 26being connected to the gate lines 22. The gate wiring also includes gatepads (not shown) connected to ends of the gate lines 22 for transmittinggate signals thereto.

A gate insulation layer 30 made of SiN_(x) is formed on top of the lowerinsulation substrate 10 to cover the gate lines 22 and the gateelectrodes 26. A semiconductor layer 40 made of a semiconductor materialsuch as amorphous silicon is formed over the gate insulation layer 30,and ohmic contact layers 55 and 56 are formed over the semiconductorlayer 40. The ohmic contact layers 55 and 56 are made of a material suchas n+ hydrogenated amorphous silicon, on which is n-type impurities at ahigh concentration, or doped silicide.

Data wiring made of a conductive material such as metal is formed overthe ohmic contact layers 55 and 56 and gate insulation layer 30. Thedata wiring includes data lines 62 formed vertically (in FIG. 1) tointersect the gate lines 22, thereby defining unit pixels P; sourceelectrodes 65 branched from the data lines 62 and extending to partiallycover the ohmic contact layer 55; and drain electrodes 66 separated fromthe source electrodes 65 and formed on top of the ohmic contact layer 56extending in a direction opposite the drain electrodes 66 with respectto the gate electrodes 26. The data wiring also includes data pads (notshown) connected to one end of the data lines 62. The data pads receiveimage signals.

A protection layer 70′ is formed over the semiconductor layer 40 andportions of the data wiring that the semiconductor layer 40 does notcover. Contact holes 76 are formed in the protection layer 70 to exposethe drain electrodes 66. Additional contact holes may be formed in theprotection layer 70 to expose the data pads, gate pads, and the gateinsulation layer 30.

A protrusion pattern 92 that is lined up vertically (in FIG. 1) with thedata lines 62 is formed over the protection layer 70. To minimize signalinterference between the data lines 62 and pixel electrodes 82 (to bedescribed hereinafter), the protrusion pattern 92 is preferably made ofan organic insulation material having a low anisotropy, and is between1-4 μm in height. The protrusion pattern 92 can be made of an organicinsulation material that is sensitive to light. Also, the protrusionpattern 92 can be formed on the same layer as the gate wiring,semiconductor layer 40, and the ohmic contact layers 55 and 56.

The pixel electrodes 82, which are made of a clear conductive materialsuch as IZO (indium zinc oxide) or ITO (indium tin oxide), are formed onthe protection layer 70. The pixel electrodes 82 are electricallyconnected to the drain electrodes 66 via the contact holes 76 of theprotection layer 70. It is possible to form auxiliary gate pads andauxiliary data pads on the same layer as the pixel electrodes 82, withthe auxiliary gate pads and auxiliary data pads contacting the gate padsand data pads, respectively, through the contact holes 76 of theprotection layer 70. With reference to FIG. 2, edges of the pixelelectrodes 82 where orientation starts are extended to partially overlapthe protrusion pattern 92 in each unit pixel P. As a result, a bentfringe field at an area A in each pixel unit P where orientation startsis identically formed to a bent alignment direction of liquid crystalmolecules 310 of a liquid crystal layer 300.

The pixel electrodes 82, with reference to FIG. 1, overlap the gatelines 22 to realize a storage capacitor, and when a storage capacitanceis insufficient, it is possible to add wiring for storage capacitance onthe same layer as the gate wiring and adjacent to the data lines 62.This will be described in more detail hereinbelow.

An upper insulation substrate 201 forms the upper substrate 200 and islocated opposite the lower insulation substrate 10. A black matrix 202having an opening pattern is formed on the upper insulation substrate201, and a color filter 203 is formed in the openings of the blackmatrix 202 partially overlapping the black matrix 202. Areas where thecolor filter 203 is formed correspond to the unit pixels P. A commonelectrode 204 is formed over the black matrix 202 and the color filter203.

Formed as innermost layers of the lower insulation substrate 10 and theupper insulation substrate 201 are alignment layers 401 and 402,respectively. The alignment layers 401 and 402 provide a force to orientthe liquid crystal molecules 310 of the liquid crystal layer 300 innearly a direction parallel to the lower and upper insulation substrates10 and 201. Here, liquid crystal of the liquid crystal layer 300 has apositive anisotropic dielectricity.

In a state where a critical voltage is applied to the pixel electrodes82 and the common electrode 204, the liquid crystal molecules 310 of theliquid crystal layer 300 adjacent to the lower and upper insulationsubstrates 10 and 201 are aligned at a specific angle with respect tothe substrates 10 and 201 due to the force of the orientation layers 401and 402, as well as the characteristics of the liquid crystal molecules310. However, as approaching an imaginary center plane, which isparallel to the substrates 10 and 201 at a center position therebetweenthe liquid crystal molecules 310 are increasingly bent as a result ofthe electric field formed between the substrates 10 and 201 (and thedecreasing influence of the orienting force of the alignment layers 401and 402) until becoming substantially perpendicular to the substrates 10and 201 at the center plane. Accordingly, the liquid crystal molecules310 form two symmetrical regions about the center plane to compensatefor a phase retardation of light passing through the liquid crystallayer 300. A wide viewing angle is obtained as a result.

Since the protrusion pattern 92 is formed at edges of the unit pixels Pwhere orientation starts (areas A), the pixel electrodes 82 at theseregions are raised since they are formed partially over the protrusionpattern 92. As a result, the electric field at areas A is bentidentically to the bent alignment direction of the liquid crystalmolecules 310 such that a smooth bent alignment of the liquid crystalmolecules 310 occurs. That is, it can prevent the broken bent alignmentof the liquid crystal molecules 310 of the prior art resulting fromopposing directions of the electric field and alignment of the liquidcrystal molecules.

In the first preferred embodiment of the present invention describedabove, liquid crystal molecules are oriented in the horizontal direction(in FIG. 1) and the protrusion pattern 92 is formed in the verticaldirection (in FIG. 1). However, if the liquid crystal molecules are setto be oriented in the vertical direction, the protrusion pattern 92 canbe formed at areas where orientation starts in the unit pixels P inparallel with the gate wiring.

FIG. 3 shows a schematic plan view of a TFT substrate used in a liquidcrystal display according to a second preferred embodiment of thepresent invention. FIG. 4 is a sectional view taken along line IV-IV′ ofFIG. 3. Since much of the structure is similar to the first preferredembodiment, only differences in structure from the first preferredembodiment will be described. Like reference numerals will be used forlike elements.

An organic insulation layer pattern 92 is formed over the protectionlayer 70. The organic insulation layer pattern 92 is formed in parallelwith the data lines 62 and has a slanted region 94 that opposes anorientation direction (shown by the arrow) at areas A. Here, if theorientation direction is perpendicular to the direction shown in FIG. 4,the organic insulation layer pattern 92 may be formed in parallel withthe gate lines 22.

Since the alignment layer 401 is formed over the organic insulationlayer pattern 92, and therefore following the slanted region 94 of theorganic insulation layer pattern 92, a depression is formed at the areasA. As a result, the liquid crystal molecules 310 adjacent to the lowerinsulation substrate 10 are aligned having a pretilt angle with respectto the surface of the lower insulation substrate 10. That is, at areasA, the liquid crystal molecules 310 are aligned having a larger pretiltangle than at other areas. Accordingly, the liquid crystal molecules 310are minimally influenced by the electric field at areas A and are stablyaligned in a bent formation even with the generation of a bent fringefield at edges of the unit pixels P. Therefore, it can prevent thebroken bent alignment of the liquid crystal molecules 310 of the priorart resulting from opposing directions of the electric field andalignment of the liquid crystal molecules.

Although the organic insulation layer pattern 92 having the slantedregion 94 is described as formed on a separate layer as the otherelements formed on the lower insulation substrate 10, it is possible forthe organic insulation layer pattern 92 to be formed on the same layeras the gate wiring, gate insulation layer 30, semiconductor layer 40,ohmic contact layers 55 and 56, data wiring, or protection layer 70.Further, a protrusion pattern can be formed to generate the slantedregion 94 at the areas A rather than elevating an area between the areasA as in the second embodiment described above. Also, a protrusion ordepression pattern can be formed at the areas A on the upper insulationsubstrate 201 to better achieve the stable bent alignment of the liquidcrystal molecules 310.

FIG. 5 shows a sectional view of a liquid crystal display according to athird preferred embodiment of the present invention. Since much of thestructure is similar to the first preferred embodiment, only differencesin structure from the first preferred embodiment will be described. Likereference numerals will be used for like elements.

As shown in the drawing, a protrusion pattern 90 is formed at areas Bwhere orientation ends. The protrusion pattern 90 results in a slantedsurface opposing an orientation direction (→). The protrusion pattern 90includes a first pattern 25 formed on the same layer as the gate wiring,a second pattern 42 formed on the same layer as the semiconductor layer40, and a third pattern 52 formed on the same layer as the ohmic contactlayers 55 and 56. The data lines 62 are formed over the third pattern52. It is possible to form the protrusion pattern 90 one, two or more ofthe patterns 25, 42, and 52, or can be formed using a separate organicinsulation layer.

In the above structure, the alignment layer 401 is formed over theprovided pattern (i.e., the protrusion pattern 90) as with the secondembodiment. Accordingly, the liquid crystal molecules 310 aligned overthe slanted surface of the protrusion pattern 90 have a pretilt anglewith respect to the substrate 10. That is, the liquid crystal molecules310 are aligned having a larger pretilt angle with respect to thesubstrate 10 at the areas B than at other areas. As a result, a stablebent alignment of the liquid crystal molecules 310 is obtained. Also, aprotrusion or depression pattern can be formed on the upper insulationsubstrate 201 to better achieve the stable bent alignment of the liquidcrystal molecules 310.

FIG. 6 shows a sectional view of a liquid crystal display according to afourth preferred embodiment of the present invention. Since much of thestructure is similar to the first preferred embodiment, only differencesin structure from the first preferred embodiment will be described. Likereference numerals will be used for like elements.

As shown in the drawing, the color filter 203 of the upper insulationsubstrate 201 is formed having a slanted surface 213 that opposes anorientation direction (→) at areas A where orientation begins. Also, aprotrusion pattern 206 is formed over the color filter 203 and the blackmatrix 202 is a protrusion pattern 206 having a slanted surface 216 thatopposes the orientation direction (→) at the areas B where orientationends.

In the above structure, the orientation layer 402 is formed over theprovided pattern as with the above second and third embodiments.Accordingly, the liquid crystal molecules 310 aligned over the slantedsurface of the protrusion pattern 90 have a pretilt angle with respectto the substrate 10. That is, the liquid crystal molecules 310 arealigned having a larger pretilt angle with respect to the substrate 10at the areas A and B than at other areas. As a result, a stable bentalignment of the liquid crystal molecules 310 is obtained both whereorientation starts and ends.

FIG. 7 shows a schematic plan view of a TFT substrate used in a liquidcrystal display having independent storage capcitance wiring accordingto a fifth preferred embodiment of the present invention. FIG. 8 is asectional view taken along line VIII-VIII′ of FIG. 7. Since much of thestructure is similar to the first preferred embodiment, only differencesin structure from the first preferred embodiment will be described. Likereference numerals will be used for like elements.

Storage capacitance wiring is formed on the same layer as the gatewiring but separated from it. The storage capacitance wiring overlapsthe pixel electrode 82. The storage capacitance wiring includes storageelectrode lines 25 formed extending in the same direction as the gateline 22 (i.e., horizontally in FIG. 7) and at two ends of a unit pixelP, and a storage electrode 27 formed vertically (in FIG. 7) tointerconnect the storage electrode lines 25. The drain electrode 66 isextended horizontally (in FIG. 7) to overlap one of the storageelectrode lines 25, thereby ensuring a sufficient storage capacitance.In the fifth embodiment, a boundary of the protrusion pattern 92 ispositioned between the data lines 62 and storage electrodes 27. However,it is possible that the boundary of the protrusion pattern 92 extendover the storage electrodes 27, and a boundary of the pixel electrode 82can be formed over the data lines 62 as in the first embodiment.

In the fifth embodiment, with the addition of the independent storagecapacitance wiring to the basic structure of the first embodiment, astable bent alignment of the liquid crystal molecules 310 is obtained.This can also be achieved through configurations outlined in the second,third and fourth embodiments. That is, the independent storagecapacitance wiring can be added also to the basic structures of thesecond, third and fourth embodiments.

Although preferred embodiments of the present invention have beendescribed in detail hereinabove, it should be clearly understood thatmany variations and/or modifications of the basic inventive conceptsherein taught that may appear to those skilled in the present art willstill fall within the spirit and scope of the present invention, asdefined in the appended claims.

1-17. (canceled)
 18. A liquid crystal display (LCD), comprising: a firstsubstrate; a second substrate facing the first substrate; a pixel regionformed between the first substrate and the second substrate; a liquidcrystal layer disposed between the first substrate and the secondsubstrate; an alignment layer formed over at least one of the firstsubstrate and the second substrate and applying an orientation force tothe liquid crystal layer; and a slant region formed on at least one ofthe first substrate and the second substrate near a first edge of thepixel region and influencing the liquid crystal layer to exhibit astable bent alignment within the pixel region.
 19. The LCD of claim 18,wherein a direction from the first edge to a second edge of the pixelregion facing the first edge is substantially the same with a directionof the orientation force.
 20. The LCD of claim 19, wherein the slantregion is formed on the first substrate.
 21. The LCD of claim 18,wherein a direction from the first edge to a second edge of the pixelregion facing the first edge is substantially opposite to a direction ofthe orientation force.
 22. The LCD of claim 21, wherein the slant regionis formed on the second substrate.
 23. The LCD of claim 18, wherein theslant region is formed by an insulating pattern formed on the firstsubstrate or the second substrate.
 24. The LCD of claim 23, wherein theinsulating pattern has a slanted edge portion.
 25. The LCD of claim 23,wherein the insulating pattern is formed of an organic insulatingmaterial.